This supercedes review-24715.
Bringing over recent bug fixes and code clean up from Rusty Jackson's local branch.

Adds an edge maintenance script to unload clients on edge servers.

Automated setting up maintenance.cfg from mkdirs.cfg settings.

Cleaned up sdputils.py - It had a logic bug, and fixed all scripts based on changes.

== Merge Details ==

Merge strategy: All the fixes to Maintenance scripts were brought in, but not the changes to active them in crontab that would enable them.

Rusty's original change had crontab changes to call maintenance scripts, and also calls to 'p4 unlock -x' as a workround to p4d bugs related to orphanged locks on edge servers. Those bugs are already fixed. Also, adding anything new to cron requires a test suite addition and doc updates. So changes to the template.crontab.combined were ignored. However, a new file was added to the Maintenace folder, sample_cron_entries.txt, to make it easy for folks to see those changes.

Rusty's original change had mkdirs.sh changes to generate maintenance.cfg. This change was enhanced during the merge. Rather than overwriting maintenance.cfg (potentially blowing away configuration for other instances), a new section for the new instance is appended to maintenance.cfg when 'mkdirs.sh <instance>' is run.

Future considerations: Before adding anything from Maintenance to cron, we need to do the following:
* Have mkdirs.sh install the Maintenance folder to the as-deployed structure under /p4/common, i.e. to /p4/common/maintenance, for HMS management compliance.
* Add tests and docs for each script called (directly or indirectly).